One apparatus for forming such corrugated board is disclosed in Australian patent 609089 [incorporated herein by reference]. Variations on this apparatus and method are disclosed in Australian patents 615053,618977, 653431 and 655076. All of these inventions follow the steps of corrugating the two mediums, bringing them into tip to tip registration, bonding them together, and then applying a liner to one or both mediums.
An alternative method is disclosed in U.S. Pat. No. 3,700,518 in which the two corrugated mediums are bonded to the liners first and then brought into tip to tip registration and bonded together.
One of the difficulties of forming paperboard structures wherein two corrugated mediums are adequately bonded together at their flute tips, is accurately aligning the peaks of the flutes along the entire length of the mediums. It will be appreciated that this is even more difficult to achieve at the web speeds of commercially used corrugating machines.
Australian patent 655076 provides a mechanical way of controlling alignment by using one driving motor for both rolls and sets of end gears at each end of the rolls. In practice this arrangement depends on the accuracy of the gearing and the initial alignment of the rolls at the beginning of each production run.
Electrical control of operations in conventional paper corrugating machines has been proposed in U.S. Pat. No. 4,174,237 to adjust the speed of single facer units to the needs of the double backer unit and in U.S. Pat. No. 4,806,183 to modify the speed of adhesive applicators to match those of the webs to which the adhesive is to be applied.
Australian patent 664018 attempted to solve the problem of flute tip to flute tip alignment in non conventional paper board by providing flute count resolvers to enable the speed of drive motors for each corrugating roll to be electronically controlled. The flute count resolvers count the number of flutes per unit time for each roll and by comparing the result the difference can be used to correct the speed of one of the two independent motors. This solution has not been used because it is difficult to precisely control the speeds of independent motors. Also the timing of the speed of the flute tips is a method with a relatively low degree of accuracy. As with other analogue devices this timing arrangement is incapable of providing the precision required to achieve precise tip to tip alignment at the speeds of commercially operated corrugating machines.